A shredder may be used to cut or tear larger objects into smaller objects. Shredding may be useful in recycling materials, or compacting them prior to disposing of them. A shredder is typically made up of a shaft with cutting surfaces used to cut materials placed into the shredder. The shaft of a shredder may be driven by various types of motors, for example, electric or hydraulic motors may be used.
FIG. 1 is a diagram of an embodiment of an electric drive shredder 100. The electric drive shredder 100 comprises two electric motors 110. The electric motors 110 are connected to a clutch mechanism 120, which may be a friction clutch. The clutch mechanism 120 acts as a guard coupling for the electric motors 110. The clutch mechanism 120 is connected to a 2-stage planetary gear drive 130 that is used to turn a shaft at a lower rpm than the rpm provided by the electric motors 110, for example, turning the shaft at 26 rpm where the electric motor is running at 1800 rpm. The gear drive 130 may be connected to a shaft (not pictured), which includes a plurality of cutting surfaces 140 used to shred materials. As described, the electric motors 110 may be configured to run at an efficient or desired speed for the particular electric motor. In the example of FIG. 1, the motor is configured to run at 1800 rpm. The electric motors 110 may also be rated for an output power based on the application. An example of a typical electric motor would operate at 150 horse-power (HP) using 3 phase 460 volt alternating current (VAC).
FIG. 2 is a diagram of an embodiment of a typical open loop hydraulic drive shredder 200. The hydraulic drive shredder 200 uses two hydraulic motors 210. The hydraulic motors 210 are powered by a hydraulic power unit 300 as depicted in FIG. 3. The hydraulic motors 210 can be configured to operate at a desired or efficient speed, such as 50 rpm. The hydraulic motors 210 are coupled to a gear box 220. The gear box 220 is used to turn a shaft powering the cutting surfaces at a lower rpm than the rpm provided by the hydraulic motors 210. For example, the gear box 220 may receive 50 rpm and output 26 rpm. The gear box 220 is typically connected to a shaft that includes a plurality of cutting surfaces used to shred materials.
FIG. 3 is a diagram of an embodiment of a hydraulic power unit 300. The hydraulic power unit 300 includes a hydraulic fluid reservoir 310, three fixed speed electric motors 320 coupled to fixed displacement pumps 330 and two hydraulic fluid coolers 340. The hydraulic power unit 300 is used to power the hydraulic motors 210 on the hydraulic drive shredder 200. The system comprising the hydraulic drive shredder 200 and the hydraulic power unit 300 may be referred to as an open loop hydraulic system.
In an open loop hydraulic system, the inlet to the pump and the return from the hydraulic motor are connected to the hydraulic fluid reservoir. The pump provides a continuous flow of hydraulic fluid to the hydraulic motors. The open loop hydraulic system typically uses less expensive constant displacement pumps.
Open loop hydraulic drive shredders provide several advantages over electric drive shredders. First, the open loop hydraulic drive shredder may be more durable than an electric drive shredder, typically hydraulic motors and pumps have a longer service life than that of the electric motors in the electric drive shredder. Second, the open loop hydraulic drive shredder may provide increased shock load protection. For example, if the shredder experiences a sudden load increase, as from the cutting shaft being stopped quickly from a jam condition, energy may be released through hydraulic fluid into the hydraulic fluid reservoir, in an electric drive system energy may be released at the clutch or may be returned to the electric motor, causing damage to drive components. Third, the open loop hydraulic drive shredder allows for a faster reversal of the direction of the hydraulic motors. Because the energy in the system can be returned to the hydraulic reservoir, the hydraulic motor may stop faster and therefore reverse faster than an electric motor which must slow down and release energy in the system by friction braking. Reversal of the motor is useful when a jam occurs in the shredder, reversing the direction of the shredder shafts allows the material causing the jam to be cleared and normal operations to continue. Lastly, all drive train parts in an open loop hydraulic drive shredder are continuously cleaned and cooled. The hydraulic fluid in the system is continuously pumped through the system and thus lubricates the parts of the drive train. In addition, the hydraulic fluid is continuously flowed through the hydraulic fluid coolers allowing heat generated in the system to dissipate into the atmosphere.
Electric drive shredders provide several advantages over open loop hydraulic drive shredders. First, electric drive shredders offer a smaller package size than the open loop hydraulic drive shredder, for example, the electric drive shredders do not require the hydraulic power unit, thus the footprint of the hydraulic reservoir and hydraulic fluid coolers would not be necessary for an electric drive system. Second, electric drive shredders offer a reduced chance of fluid leaks because of the reduction in hydraulic fluid used by the system. Third, electric drive shredders provide a lower noise solution relative to open loop hydraulic drive shredders. The electric drive shredder typically requires fewer motors than the open loop hydraulic drive shredders and is therefore quieter. Because the electric drive shredder typically requires fewer motors than the open loop hydraulic drive shredders, it is usually more energy efficient.
It would be desirable to design an industrial shredder that realizes the advantages of both electric drive shredders and open loop hydraulic shredders.